Power steering pump having electronic bypass control

ABSTRACT

A power steering pump comprises a housing that includes a bore, a fluid discharge port that supplies pumped fluid into the bore, and a fluid bypass port for recycling excess fluid to the pumping elements. A flow control valve is slideably received in the bore and regulate the size of the inlet to the fluid bypass port. The pump includes a solenoid assembly that has a plunger that is operatively connected to the flow control valve. By adjusting the magnitude of the current to the electromagnetic coil of the solenoid assembly, the position of the flow control valve is varied to increase or decrease fluid flow to the fluid bypass port and thereby regulate the output from the pump.

RELATED APPLICATIONS

The present patent document claims the benefit of the filing date under35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No.60/407,918, filed Sep. 3, 2002, which is hereby incorporated byreference.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a power steering pump wherein the fluid outputis controlled by recycling a portion of the pumped fluid through abypass port within the pump. More particularly, this invention relatesto such power steering pump that includes a valve for controlling thesize of the inlet to the bypass port.

BACKGROUND OF THE INVENTION

A power steering system of an automotive vehicle comprises a pump forproviding hydraulic fluid under pressure. A typical power steering pumpcomprises a rotor having retractable vanes and rotating within a camchamber. During operation, hydraulic fluid is drawn into the cam chamberfrom a fluid suction passage and pumped out under pressure to a fluiddischarge port. The rotor is driven by the engine through a belt andpulley. As the speed of the engine increases, the volume of fluid pumpedby the rotor also increases, and exceeds the volume required by thepower steering system for optimum operation. The output from the pump ismaintained at an optimum value by recycling a portion of the pumpedfluid through a bypass port in the pump housing, so that pumped fluid isdiverted from the outlet and returned to the suction passage. At lowengine speeds, the bypass port is closed so that the entire volume ofpumped fluid is outputted from the pump. However, at higher enginespeeds, the bypass port is open for recycling as much as 90% of thepumped fluid.

U.S. Pat. No. 5,887,612, issued Bleitz et al. in 1999, shows amechanical valve for opening and closing a fluid bypass port to regulatethe output from the pump. For this purpose, the housing defines a borethat communicates with a fluid discharge port from the pumping chamberand with the fluid bypass port. The outlet from the pump is located atone end of the bore and comprises a constricted passage to limit fluidoutput. Within the bore, a flow control valve slides to open and closethe bypass port. The valve is biased in the closed position by a spring.During operation, particularly at higher engine speeds, the increasedfluid volume acts upon the valve to contract the spring and open thebypass port, thereby diverting excess fluid from the outlet andrecycling fluid through the bypass port.

Because of the restrictive outlet, the pump maintains a relativelyconstant output volume. Since the output is restricted, the excess fluidtends to push the spring-biased valve into the fully open position athigher engine speeds. Under certain conditions, it is desired toincrease the output from the pump to improve performance of thissteering system. It is known to provide a variable volume power steeringpump wherein the size of the cam chamber is varied. During operation,the volume of pumped fluid is regulated by adjusting the cam chamber, sothat a bypass port is not needed or provided. However, mechanisms forcontrolling the size of the cam chamber are complicated and requireadditional in-pump components and controls.

Therefore, a need exists for a power steering pump having a variableoutput, in which a portion of the pumped fluid is recycled through abypass within the pump, and further in which the portion through thebypass is controlled to obtain a desired output from the pump.

BRIEF SUMMARY OF THE INVENTION

In accordance with this invention, a power steering pump comprises ahousing defining a bore having an axis, a fluid discharge portcommunicating with the bore at a first axial location, and fluid bypassport communicating with the bore at a second axial location. A flowcontrol valve is slideably received in the bore and regulates the inletfor admitting fluid to the fluid bypass port. In accordance with thisinvention, electrical means are provided for sliding the flow controlvalve to vary the size of the inlet to the fluid discharge port andthereby increases or decrease fluid flow to the fluid bypass port, toadjust the output from the pump.

In one aspect of this invention, the pump includes a solenoid assemblythat comprises a plunger that is connected to the flow control valve andis responsive to an applied electromagnetic field. An electromagneticcoil is provided outside the bore for applying an electromagnetic fieldto actuate the plunger. The position of the flow control valve dependsupon the magnitude of the applied electromagnetic field, which in turnis regulated by the flow of current to the electromagnetic coil. Bycontrolling electrical current to the electromagnetic coil, the size ofthe inlet to the bypass port is adjusted to control the proportion offluid recycled through the bypass port. In this manner, the output fromthe pump may be electronically controlled to optimize performancedepending upon driving conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be further described with reference to the followingdrawings wherein:

FIG. 1 is a cross-sectional view, partially in schematic, of a powersteering pump in accordance with this invention and showing a flowcontrol valve in an open bypass position; and

FIG. 2 is a cross-sectional view of a portion of a power steering pumpin FIG. 1, showing the elements thereof in a bypass closed position.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with a preferred embodiment of this invention, referringto FIGS. 1 and 2, there is depicted a power steering pump 10 forsupplying pressurized fluid for a power steering system of an automotivevehicle. Pump 10 comprises a housing 12, preferably formed of aluminumalloy. Housing 12 contains pumping element, showing schematically, thatinclude a rotor 14 that propels retractable vane 16 within a cam chamber18. Housing 12 defines a fluid discharge port 20 that carries fluidunder pressure from cam chamber 18, as indicated by arrow 22. Thehousing also defines a suction passage, indicated by arrow 24, fordelivering fluid to cam chamber 18. During operation, rotor 14 is drivenby the automotive engine via a belt and pulley arrangement. Fluid ispumped under pressure to discharge port 20 and exists through an outlet27 in adapter 26, as output 28. Adapter 26 is connected through tubingto a rotary valve and steering gear of the power steering system. Fluidis returned to the pump through a return line (not shown) connected tosuction passage 24 and is, in turn, drawn into cam chamber 18.

In accordance with this invention, the volume of output 28 from the pumpis controlled by recycling a portion of the pumped fluid through abypass port 30 to suction passage 24, as indicated by arrow 32. For thispurpose, a bore 34 is provided in housing 12 and has a central axis 36.In the embodiment depicted in the Figs., bore 34 extends partiallythrough the housing and includes an open end adjacent outlet 27. Bore 34also communicates with discharge port 20 at a first axial location andwith bypass port 30 at a second axial location that is axially spacedfrom the first location. In this embodiment, fluid discharge port 20 islocated nearer the open end of bore 34 relative to bypass port 30.Alternately, the passages within the housing may be configured so thatthe bypass port is nearer the bore open end than the fluid dischargeport.

Fluid to bypass port 30 is controlled by a flow control valve assemblythat includes a flow control valve 38 slideably received in sleeve 40inserted in bore 34. Sleeve 40 comprises openings 42 and acircumferential groove 44 in fluid communication with fluid dischargeport 20 and also comprises openings 46 and circumferential groove 48 influid communication with fluid bypass port 30. Valve 38 comprisesopenings 52 and circumferential groove 54 that communicate with openings42 in sleeve 40, and 38 also includes openings 56 and a circumferentialgroove 58 adapted for communicating with openings 46 in sleeve 40. Acentral axial fluid passage 50 communicates with outlet passages 27.Valve 38 slides between a fully open position depicted in FIG. 1 and aclosed position depicted in FIG. 2. During operation, fluid from fluiddischarge port 20 is distributed by grooves 44 to flow through openings42 into groove 54 and through opening 52 into central passage 50, andfrom central passage 50 through outlet 27. It is pointed out that groove54 is axially widened, and that valve 38 includes multiple openings 52that are axially spaced to provide continuous fluid communicationbetween fluid discharge port 20 and central passage 50 despite movementof valve 38 between the fully open and closed positions. Moreover,during operation, when valve 38 is open, for example, in the fully openposition depicted in FIG. 1, fluid flows from central passage 50 throughopenings 46 and groove 58 of valve 38, and thereafter through openings56 and groove 48 to bypass port 30. This permits an excess portion ofthe pumped fluid to be recycled through bypass port 30 to control theoutput from the pump. In the closed position shown in FIG. 2, valve 38slides to axially displace openings 56 relative to openings 46 in sleeve40, where the circumferential surface of valve 38 closes the openings 46in sleeve 40 to prevent fluid flow to bypass port 30. Thus, in thisembodiment, openings 46 and 56 cooperate to define the inlet to fluidbypass port 30. It is an advantage of this invention that the positionof valve 38 maybe varied between the fully open and the closed positionto vary the size of the inlet to increase or decrease fluid flow to thefluid bypass port and thereby decrease or increase, respectively, thevolume of pump output 28.

In accordance with this invention, valve 38 is opened and closed by asolenoid assembly 60 that includes an electrical coil 62 for generatingan electrical field. Coil 62 is disposed about a conduit extension 64that is connected at one end to sleeve 40 and at the opposite end toadaptor 26, using O-ring 66 and 68 to seal the connections. A coilspring 70 is disposed between valve 38 and adaptor 26 within extension64 and biases the valve in the open position. Electrical connections tocoil 62 are made by terminal 72 protected by a shield 74. A threadedconnector 76 is provided for mounting to the housing 12. It is pointedout that the elements, including valve 38, sleeve 40, coil 62, andadaptor 26, are assembled to form a single flow control assembly thatmay be readily installed into housing 12 as a single component. Further,in the event that a repair of pump 10 is necessary, the flow controlassembly may be readily removed and replaced, thereby reducing the timeand expense required for such repair.

In the depicted embodiment, prior to operation, valve 38 is biased inthe fully open position shown in FIG. 1 by coil spring 70. In the fullyopen position depicted in FIG. 1, pumped fluid from the pumpingelements, including rotors 14, vanes 26 and cam chamber 18, deliverpumped fluid to fluid discharge port 20. The pumped fluid flows throughopenings 42 in sleeve 40 and openings 52 in valve 38 into centralpassage 50. A portion of the fluid flows through central passage 50 andextension 64 and outlet 27 to provide the output 28 for the pump. Excessfluid flows from passage 50 through the inlet formed by openings 56 invalve 38 and openings 46 in sleeve 40 into bypass port 30 and arecombined with returning fluid 24, thereby recycling the fluid within thepump.

During operation, rotor 14 is driven by the engine of an automotivevehicle by a belt and pulley arrangement. The pumping elements,including rotors 14, vanes 26 and cam chamber 18, are preferably sizedso that, at low engine speeds, the volume of pumped fluid is equal tothe desired output 28 of pump 10. Under these circumstances, it isdesired that no portion of the pumped fluid be returned through bypassport 30. This is accomplished by positioning valve 38 to close bypassport 30 from fluid communication with fluid discharge port 20, as shownin FIG. 2. To close valve 38, terminal 72 are connected to an electricalpower supply, and current is conducted through coil 62 to generate anelectromagnetic field within extension 64. Valve 38 is preferably formedof steel or other suitable magnetizeable material and thus serves as theplunger for the solenoid assembly. Thus, valve 38 moves axially inresponse to the applied electrical field to the closed position shown inFIG. 2. The movement of valve 38 contracts spring 68. Fluid flows fromfluid discharge port 20 through openings 42 in sleeve 40 and openings 52in valve 38 into passage 50. With the valve in the closed position, theentire volume of fluid flows through passage 50 and outlet passage 27and provides output 28 for the pump.

It is an advantage of this invention that the position of valve 38 maybe adjusted to vary the size of the inlet to the bypass port and therebycontrol the pump output 28 to optimize performance to the power steeringsystem for particular driving conditions. By way of example, an optimumpump output may be determined based upon vehicle speed, steering wheelrate, and fluid pressure within the power steering system. For thispurpose, a control module may be provided for regulating current toelectromagnetic coil 62. The control module receives input, for example,for vehicle speed and steering signals, and determines an optimum systempressure or fluid volume using a look-up table or algorithm. The controlmodule then regulates current to the electromagnetic coil 62 to adjustthe position of the flow control valve. In this manner, the flow controlvalve may be moved to increase or decrease the size of the inlet to thebypass port and so increase or decrease the proportion of pumped fluid.Opening the valve increases flow fluid through the bypass port anddecreases output 28, whereas closing the valve decreases flow to thebypass port and increases output 28. By making appropriate adjustmentsto the position of the flow control valve and thus to the size of theinlet to the fluid bypass port, an optimum output may be obtained forparticular driving conditions.

Therefore, this invention provides a power steering pump wherein theflow control valve controls the inlet to the fluid bypass port andvaries the size of the inlet to thereby regulate the volume of fluidflowing through the bypass port. This is in marked contrast toconventional pumps having mechanical valves that restrict flow throughthe outlet, thereby increasing pressure within the bore to fully openthe valve and divert excess fluid to the bypass. The position of theflow control valve may be adjusted electronically by a solenoid assemblyconnected to the valve that opens and closes the valve in response toelectric current to an electromagnetic coil. The solenoid assembly isreadily mounted on the pump and connected to the electronic controlsystem for the automotive vehicle. By adjusting the fluid volume throughthe bypass port, the flow control system with this invention permits theoutput of the power steering pump to be adjusted for a desired value.

In the described embodiment, the flow control valve was disposed withina sleeve and includes openings that cooperate with openings in thesleeve to define the inlet to the fluid bypass port. Alternately, thevalve may open and close the opening of the fluid bypass port toregulate the size of the inlet without requiring a sleeve. Also, whereasthe flow control valve in the described embodiment slides axially, in analternate embodiment, the flow control valve may be rotated to open andclose the inlet to the bypass port. This may be accomplished by a stepmotor or other suitable electronic actuator capable of varying theangular orientation of the valve.

While this invention has been described in terms of certain embodimentthereof, it is not intended to be so limited, but rather only to theextent set forth in the claims that follow.

1. A power steering pump comprising: a housing defining a bore having an axis; a fluid discharge port communicating with the bore at a first axial location; a fluid bypass port communicating with the bore at a second axial location; a flow control valve slideably received in the bore, and providing an inlet to the bypass port; electrical means for sliding the flow control valve within the bore to vary the size of the inlet to the bypass port.
 2. A power steering pump in accordance with claim 1 wherein the valve slides between a closed position wherein the valve closes the inlet to prevent communication between the fluid discharge port and the fluid bypass port, and an open position wherein fluid flows from the bore to the fluid discharge port through the inlet.
 3. A power steering pump in accordance with claim 2 wherein the flow control valve slides axially between the open position and the closed position.
 4. A power steering pump in accordance with claim 2 wherein the flow control valve rotates between the open position and the closed position.
 5. A power steering pump in accordance with claim 2 further comprising means for biasing the valve in the open position.
 6. A power steering pump in accordance with claim 1 further comprising pumping elements disposed within the housing, said pumping elements comprising a cam chamber and a rotor having retractable vanes disposed within the cam chamber.
 7. A power steering pump comprising: a housing defining a bore having an axis, an outlet adjacent one end of the bore, a fluid discharge port communicating with the bore at a first axial location, and a fluid bypass port communicating with the bore at a second axial location; pumping elements disposed within the housing for pumping fluid to said fluid discharge port and communicating with said bypass port for drawing fluid therefrom; a flow control valve slideably received in the bore and defining an inlet to the bypass port; a plunger operatively connected to the flow control valve and responsive to an applied electromagnetic field to slide the flow control valve between a closed position wherein the flow control valve closes the inlet and an open position wherein fluid flows from the bore to the fluid bypass port through the inlet; a spring operatively coupled to the flow control valve for biasing the flow control valve in the open position; an electromagnetic coil for applying an electromagnetic field to the plunger to vary the size of the inlet to the fluid bypass port.
 8. A power steering pump in accordance with claim 7 wherein the pumping elements comprise a cam chamber and a rotor having retractable vanes disposed within the cam chamber.
 9. A power steering pump in accordance with claim 7, further comprising a sleeve received in the bore and having an opening communicating with the fluid bypass port, and wherein the flow control valve is slideably received within the sleeve and includes an opening that cooperates with the opening in the sleeve to define the inlet to the fluid bypass port.
 10. A power steering pump comprising: a housing defining a bore having an axis and open end, a fluid discharge port communicating with the bore at a first axial location proximate to the open end, and a fluid bypass port communicating with the bore at a second axial location; pumping elements disposed within the housing and adapted for drawing fluid from the fluid bypass port and pumping fluid to said fluid discharge port; a sleeve received in bore and having an opening communicating with the fluid bypass port; a flow control valve slideably received in the bore having an opening, said flow control valve being slideable between a closed position that closes the opening in the sleeve and an open position wherein the opening in the flow control valve cooperates with the opening in the sleeve to define an inlet to allow fluid flow to the fluid bypass port; a tubular extension sealing mounted onto the housing at said open end; a plunger disposed within the tubular extension and operatively connected to the flow control valve, said plunger being responsive to an applied electromagnetic field to slide the valve axially between the closed position and the open position and to vary the position of the flow control valve in the open position to vary the size of the inlet; a spring engaging the plunger for biasing the flow control valve in the open position; an electromagnetic coil disposed about the extension and adapted for applying an electromagnetic field to the plunger.
 11. A power steering pump in accordance with claim 10 wherein the extension includes an end cap, and wherein plunger includes a rear end adjacent the end cap and a pressure equalization passage extending from the rear end and communicating with fluid adjacent the flow control valve. 